Vaccination gun

Abstract

In a vaccination gun provided with a piston pump for the vaccine and a gas-propelled motor for the vaccine pump, the drive motor is arranged with one end thereof coupled to the vaccine pump. In the handle grip of the vaccination gun, a coupler connects a propellant gas cylinder, through a trigger, or locking valve, to the drive motor. In order to assure that the injection pressure of the propellant gas remains between about 270 and 300 bar regardless of the pressure in the cylinder, there is provided a pressure regulation chamber between the coupler and the locking valve, which chamber is provided with a flap valve coupled to a hollow shaft. The shaft moves within a cylindrical portion of the chamber and is provided with radial borings for permitting the propellant gas to pass between the main part of the chamber and the cylindrical portion thereof.

What is claimed is: 
     
       1. In a vaccination gun of the type having a vaccine piston pump, drive motor means for driving the pump, said drive motor means being operated by a propellant gas, locking valve means for selectively admitting said propellant gas to said drive motor means, container means for holding said propellant gas, coupler means for coupling said container means with said locking valve means, and housing means housing said container means and coupler means and forming a gun grip; the improvement wherein said coupler means includes a chamber fluidically connected between said container means and said locking valve means, flap-valve means loosely a chamber and slidably mounted in said chamber and dividing said chamber into a first portion communicating with said container means and a second portion communicating with said locking valve means, said flap-valve means being responsive to pressure released by said locking valve means to move from a first position in said chamber adjacent said container means to a second position in said chamber adjacent said locking means, said coupler means including means for providing a gas leak from said first portion to said second portion of said chamber; and wherein said chamber includes means for sealing against said flap-valve means when in said second position thereby preventing gas flow from said first portion to said second portion except through said means for providing a gas leak whereby, pressure between the first and second portions of the chamber is equalized after said flap-valve means is sealed against said sealing means; and biasing means biasing said flap valve means away from said sealing means and toward said first position after said pressure is equalized. 
     
     
       2. A vaccination gun according to claim 1, wherein said second portion of said chamber is diametrically smaller than the first portion and said flap-valve means includes a piston loosely and slidably mounted in said first portion and a hollow shaft extending axially from said piston and being loosely and slidably mounted in said second portion and wherein said hollow shaft includes at least one radial bore communicating the interior of said shaft with said second portion of said chamber. 
     
     
       3. A vaccination gun according to claim 2, wherein said means for providing a leak includes a bore extending through said piston into said hollow shaft to equalize pressure on opposite sides of said flap-valve means. 
     
     
       4. A vaccination gun according to claim 2, wherein said biasing means includes a pressure spring mounted within said hollow shaft and between said piston and chamber. 
     
     
       5. A vaccination gun according to claim 1, wherein said means to provide a leak includes a bore extending through said flap-valve means to equalize pressure on opposite sides of said flap-valve means. 
     
     
       6. A vaccination gun according to claim 1 or 2, wherein said means for providing a gas leak includes a bypass line around said chamber connecting said first portion to said second portion to equalize the pressure on opposite sides of said flap-valve means. 
     
     
       7. A vaccination gun according to claim 5 or 6 wherein said means providing a gas leak includes mechanical trigger means for urging said flap-valve means toward said first position thereby providing a gas leak between said flap-valve means and said chamber.